1. Field of the Invention
The present invention relates to light emitting diode devices. In particular the invention relates to illumination systems using LEDs along with various materials to convert the light emitted from the LEDs.
2. Description of Related Art
Light emitting diodes (LEDs) are becoming a viable alternative to conventional light sources in many applications. For years, LEDs were used as indicator lights because of their long life, reliability and energy efficiency. Most recently, LEDs have been making a big impact in the field of illumination. LEDs have been exponentially increasing in brightness over the years, leading to their acceptance into the field of illumination.
While many LEDs provide nearly 100,000 hours of performance, white LEDs have significantly shorter lives. Both the expected lifetime and the lumen maintenance over the lifetime are significantly reduced compared to conventional non-white high brightness LEDs. There may be several reasons for this drop-off in performance. The white LED package uses a blue or ultraviolet die to pump an active phosphor impregnated in the die, package or epoxy used in the package of the LED to produce white light. The phosphor converts the blue or ultraviolet wavelengths produced by the die into a white light. The die itself usually produces a rather narrow spectrum of blue light and the phosphor down converts this energy to longer wavelength energy. The resulting spectrum is shifted from the narrow blue towards the middle of the visible spectrum and the spectrum is typically broadened. White LEDs are available through companies such as Nichia. Because of imperfections in this down conversion, the white LEDs produce a very blue-white light meaning the color temperature of the illumination and the quality of the light is not acceptable for many general illumination applications.